Multiple actuator and linkage system

ABSTRACT

An actuator system comprising a shared link arranged to pivot about a first axis relative to a reference structure, a controlled element arranged to pivot about a second axis relative to the reference structure, a first member arranged to pivot about a third axis relative to the shared link and a fourth axis relative to the controlled member, a first actuator arranged to control a first variable distance between the third axis and fourth axis, a second member arranged to pivot about a fifth axis relative to the shared link and a sixth axis relative to the controlled element, a second actuator arranged to control a second variable distance between the fifth axis and the sixth axis, the system configured such that a change in the first variable distance causes rotation of the controlled element about the second axis when the second variable distance is constant and vice versa.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of actuatorsystems, and more specifically to an electromechanical redundantactuator.

BACKGROUND ART

Redundant actuator systems are generally known. These systems typicallyarrange multiple actuators in a way in which their displacement issummed, or their torque is summed.

BRIEF SUMMARY OF THE INVENTION

With parenthetical reference to the corresponding parts, portions orsurfaces of the disclosed embodiment, merely for the purposes ofillustration and not by way of limitation, the present inventionprovides an actuator system comprising a shared link (121) configuredand arranged for pivotal movement about a first axis (131) relative to areference structure (120), a controlled element (125) configured andarranged for pivotal movement about a second axis (126) relative to thereference structure (120), a first member configured and arranged forpivotal movement about a third axis (134) relative to the shared linkand configured and arranged for pivotal movement about a fourth axis(136) relative to the controlled element, the third axis (134) and thefourth axis (136) offset by a first variable distance (L1), a firstactuator (140) configured and arranged to control the first variabledistance, a second member configured and arranged for pivotal movementabout a fifth axis (133) relative to the shared link and configured andarranged for pivotal movement about a sixth axis (135) relative to thecontrolled element, the fifth axis (133) and the sixth axis (135) offsetby a second variable distance (L2), a second actuator (141) configuredand arranged to control the second variable distance, and the actuators,shared link, first member, second member and controlled elementoperatively configured and arranged such that a change in the firstvariable distance rotates the controlled element (125) about the secondaxis when the second variable distance is constant, and a change in thesecond variable distance rotates the controlled element (125) about thesecond axis when the first variable distance is constant.

The first, second, third, fourth, fifth and sixth axis may besubstantially parallel to each other. The fourth axis and the sixth axismay be positioned on opposite sides of an imaginary line through thethird axis and the second axis. The fourth axis (536) and the sixth axis(535) may be positioned on the same side of an imaginary line throughthe third axis and the second axis. The third axis may be coincidentwith the fifth axis. The first axis may be coincident with the thirdaxis. The first axis may be coincident with the fifth axis.

The system may further comprise a brake (381) configured and arranged tolimit rotation of the shared link about the first axis. The actuatorsystem may further comprise a brake configured and arranged to hold thefirst variable distance or the second variable distance constant. Thesystem may further comprise a spring (382) configured and arranged tobias rotation of the shared link about the first axis. The system mayfurther comprise a spring configured and arranged to bias rotation ofthe controlled element about the second axis. The system may furthercomprise a damper (383) configured and arranged to dampen rotation ofthe shared link about the first axis. The first member may comprise alinear spindle (296).

The first member may comprise a first link (152) and a second link(146), the first link (152) configured and arranged for pivotal movementabout the third axis (134), the second link (146) configured andarranged for pivotal movement about the fourth axis (136), and the firstlink (152) configured and arranged for pivotal movement about a seventhaxis (194) relative to the second link (146). The first actuator maycomprise a rotary actuator (140) mounted on the shared link (121) andconfigured and arranged to control rotary movement between the sharedlink (121) and the first link (152). The second member may comprise athird link (153) and a fourth link (147), the third link (153)configured and arranged for pivotal movement about the fifth axis (133),the fourth link (147) configured and arranged for pivotal movement aboutthe sixth axis (135), and the third link (153) configured and arrangedfor pivotal movement about an eighth axis (193) relative to the fourthlink (147). The second actuator may comprise a rotary actuator (141)mounted on the shared link (121) and configured and arranged to controlrotary movement between the shared link (121) and the third link (153).

The seventh axis (494) and the eighth axis (493) may be on the same sideof an imaginary line through the third axis and the second axis. Theseventh axis (194) and the eighth axis (193) may be on opposite sides ofan imaginary line through the third axis and the second axis. The springmay be selected from a group consisting of a torsional spring, a linearspring, and a flexure. The damper may be selected from a groupconsisting of a linear damper and a rotary damper. The first actuatorand the second actuator may comprise a stepper motor or a permanentmagnet motor. The first actuator may comprise a motor output shaft andmay further comprise a planetary gear stage between the motor outputshaft of the first member. The controlled element may be a shaft or anaircraft control surface. The controlled element may be selected from agroup consisting of a wing spoiler, a flap, a flaperon and an aileron.The reference structure may be selected from a group consisting of anactuator frame, an actuator housing, and an airframe.

In another aspect, the invention provides an actuator system comprisingan element (125) configured for rotary movement about a first axis (126)relative to a reference structure (120), a linkage system connected tothe element (125) and the reference structure (120), the linkage systemhaving a link (121) configured for rotary movement about a second axis(131) relative to the reference structure, the first axis and the secondaxis being substantially parallel and operatively offset a substantiallyconstant distance, the linkage system configured and arranged such thata first angle of rotation (161) between the element and the referencestructure may be driven independently of a second angle of rotation(162) between the link (121) and the reference structure (120), a firstactuator (140) connected to the linkage system and arranged to power afirst degree of freedom (164) of the linkage system, a second actuator(141) coupled to the linkage system and arranged to power a seconddegree of freedom (163) of the linkage system, the first degree offreedom and the second degree of freedom being independent degrees offreedom, wherein the first actuator (140) may be configured and arrangedto drive rotation of the element about the first axis when the seconddegree of freedom may be operatively locked.

The element may be connected to the reference structure through abearing. The link may be connected to the reference through a bearing.The linkage system may comprise five links (152, 153, 146, 147 and 121).The linkage system may be connected to the element through a pivotjoint. The first actuator (140) may power an angle (164) between twoconnected links (121/152) in the linkage system. The first actuator maypower a distance between two joints (134/136) in the linkage system. Thefirst actuator may comprise a rotary actuator and the rotary actuatormay have an axis of rotation substantially the same as the second axis.The first actuator may comprise a rotary motor or an electric motor. Thefirst actuator may comprise a planetary gear. The first actuator may bemounted on the link. The first actuator may be connected to thereference through a pivot connection. The system may further comprise abrake configured and arranged to limit rotation of the link about thesecond axis. The system may further comprise a brake configured andarranged to hold one degree of freedom of the linkage system constant.The system may further comprise a spring configured and arranged to biasrotation of the link about the second axis. The system may furthercomprise a spring configured and arranged to bias rotation of theelement about the first axis. The system may further comprise a damperconfigured and arranged to dampen rotation of the link about the secondaxis. The linkage system may comprise a linear spindle. The spring maybe selected from a group consisting of a torsional spring, a linearspring, and a flexure. The damper may be selected from a groupconsisting of a linear damper and a rotary damper. The first actuatorand the second actuator may comprise a stepper motor or a permanentmagnet motor. The element may be selected from a group consisting of ashaft and an aircraft control surface. The element may be selected froma group consisting of a wing spoiler, a flap, a flaperon and an aileron.The reference structure may be selected from a group consisting of anactuator frame, an actuator housing, and an airframe.

In another aspect, the invention provides an actuator system comprisingan element (125) configured for rotary movement about a first pivot(126) relative to a reference structure (120), a first linkage (146,152, 121) connected to the element at a first element connection (136)offset from the first pivot (126) and extending from the first elementconnection (136) to a first reference connection (131) of the referenceoffset from the first pivot (126), a second linkage (147, 153, 121)connected to the element at a second element connection (135) offsetfrom the first pivot (126) and extending from the second elementconnection (135) to a second reference connection (131) of the referenceoffset from the first pivot (126), the element (125) and the firstlinkage forming a first system linkage having at least two independentdegrees of freedom, the element (125) and the second linkage forming asecond system linkage and having at least two independent degrees offreedom, a first motor (140) connected to the first linkage, a secondmotor (141) connected to the second linkage and movable independent ofthe first motor, the first linkage and the second linkages coupled so asto share a degree of freedom, the first motor (140) configured andarranged to power a degree of freedom in the first linkage, the secondmotor (141) configured and arranged to power a degree of freedom in thesecond linkage, and one of the motors (140) configured and arranged tomove the element (125) relative to the reference (120) when the other ofthe motors (141) operatively locks the powered degree of freedom.

In another aspect, the invention provides an actuator comprising ashared link (121) pivotally connected (131) to a reference structure(120), a controlled element (125) pivotally connected (126) to areference structure (120), a first electric motor (140) mounted on theshared link (121), the first electric motor (140) having a drive shaft(152) coupled to a proximal end of an upper link (46), a second electricmotor (141) mounted on the shared link (121), the second electric motor(141) having a drive shaft (153) coupled to a proximal end of a lowerlink (147), the upper link (146) having a distal end pivotally connected(136) to the controlled element (125), the lower link having a distalend pivotally connected (135) to the controlled element (125), wherebyactuation of one of the motors while holding the other of the motorsstill causes rotation of the controlled link (125) relative to thereference structure (120).

In another aspect, the invention provides a method of controlling anactuator system comprising the steps of providing an actuator systemcomprising a shared link (121) configured and arranged for pivotalmovement about a first axis (131) relative to a reference structure(120), a controlled element (125) configured and arranged for pivotalmovement about a second axis (126) relative to the reference structure(120), a first member configured and arranged for pivotal movement abouta third axis (134) relative to the shared link and configured andarranged for pivotal movement about a fourth axis (136) relative to thecontrolled element, the third axis (134) and the fourth axis (136)offset by a first variable distance (L1), a first actuator (140)configured and arranged to control the first variable distance, a secondmember configured and arranged for pivotal movement about a fifth axis(133) relative to the shared link and configured and arranged forpivotal movement about a sixth axis (135) relative to the controlledelement, the fifth axis (133) and the sixth axis (135) offset by asecond variable distance (L2), a second actuator (141) configured andarranged to control the second variable distance, and the actuators,shared link, first member, second member and controlled elementoperatively configured and arranged such that a change in the firstvariable distance rotates the controlled element (125) about the secondaxis when the second variable distance may be constant, and a change inthe second variable distance rotates the controlled element (125) aboutthe second axis when the first variable distance is constant, andproviding power to the first actuator and the second actuatorsimultaneously such that the controlled element (125) is rotated aboutthe second axis and the shared link (121) is held constant about thefirst axis. The first actuator and the second actuator may be providedpower in opposition to each other, whereby backlash in the actuatorsystem may be minimized.

In another aspect, the invention provides a method of controlling anactuator system comprising the steps of providing an actuator systemcomprising a shared link (121) configured and arranged for pivotalmovement about a first axis (131) relative to a reference structure(120), a controlled element (125) configured and arranged for pivotalmovement about a second axis (126) relative to the reference structure(120), a first member configured and arranged for pivotal movement abouta third axis (134) relative to the shared link and configured andarranged for pivotal movement about a fourth axis (136) relative to thecontrolled element, the third axis (134) and the fourth axis (136)offset by a first variable distance (L1), a first actuator (140)configured and arranged to control the first variable distance, a secondmember configured and arranged for pivotal movement about a fifth axis(133) relative to the shared link and configured and arranged forpivotal movement about a sixth axis (135) relative to the controlledelement, the fifth axis (133) and the sixth axis (135) offset by asecond variable distance (L2), a second actuator (141) configured andarranged to control the second variable distance, and the actuators,shared link, first member, second member and controlled elementoperatively configured and arranged such that a change in the firstvariable distance rotates the controlled element (125) about the secondaxis when the second variable distance may be constant, and a change inthe second variable distance rotates the controlled element (125) aboutthe second axis when the first variable distance is constant, andproviding power to the first actuator and the second actuatorsimultaneously such that the shared link (121) is rotated about thefirst axis, whereby a mechanical advantage between the first actuatorand rotation of the shared link is adjusted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevation view of a first embodiment of the actuatorsystem.

FIG. 2 is a right side view of the actuator system shown in FIG. 1 in afirst horizontal configuration.

FIG. 3 is a view of the actuator system shown in FIG. 2 in a first dualmotor actuated configuration.

FIG. 4 is a view of the actuator system shown in FIG. 2 in a second dualmotor actuated configuration.

FIG. 5 is a view of the actuator system shown in FIG. 2 in a jam failureactuated configuration.

FIG. 6 is a view of the actuator system shown in FIG. 2 in a modifiedperformance actuated configuration.

FIG. 7 is a front elevation view of a second embodiment of the actuatorsystem.

FIG. 8 is a right side view of the actuator system shown in FIG. 7.

FIG. 9 is a right side view of a third embodiment of the actuatorsystem.

FIG. 10 is a right side view of a fourth embodiment of the actuatorsystem.

FIG. 11 is a front elevation view of a fifth embodiment of the actuatorsystem.

FIG. 12 is a right side view of the actuator system shown in FIG. 11.

FIG. 13 is a top view of the actuator system shown in FIG. 11.

FIG. 14 is a front elevation view of a sixth embodiment of the actuatorsystem.

FIG. 15 is a right side view of the actuator system shown in FIG. 14.

FIG. 16 is a top view of the actuator system shown in FIG. 14.

FIG. 17 is a vertical sectional view of the actuator system shown inFIG. 16, taken generally on line 17-17 of FIG. 16.

FIG. 18 is a front partial perspective view of a seventh embodiment ofthe actuator system.

FIG. 19 is a rear partial perspective view of the actuator system shownin FIG. 18.

FIG. 20 is a front view of the actuator system shown in FIG. 18.

FIG. 21 is a rear view of the actuator system shown in FIG. 18.

FIG. 22 is a horizontal sectional view of the actuator system shown inFIG. 21, taken generally on line 22-22 of FIG. 21.

FIG. 23 is a top view of the actuator system shown in FIG. 18.

FIG. 24 is a vertical sectional view of the actuator system shown inFIG. 23, taken generally on line 24-24 of FIG. 23.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

At the outset, it should be clearly understood that like referencenumerals are intended to identify the same structural elements, portionsor surfaces consistently throughout the several drawing figures, as suchelements, portions or surfaces may be further described or explained bythe entire written specification, of which this detailed description isan integral part. Unless otherwise indicated, the drawings are intendedto be read (e.g., cross-hatching, arrangement of parts, proportion,degree, etc.) together with the specification, and are to be considereda portion of the entire written description of this invention. As usedin the following description, the terms “horizontal”, “vertical”,“left”, “right”, “up” and “down”, as well as adjectival and adverbialderivatives thereof (e.g., “horizontally”, “rightwardly”, “upwardly”,etc.), simply refer to the orientation of the illustrated structure asthe particular drawing figure faces the reader. Similarly, the terms“inwardly” and “outwardly” generally refer to the orientation of asurface relative to its axis of elongation, or axis of rotation, asappropriate.

Referring now to the drawings, and more particularly to FIGS. 1 and 2thereof, this invention provides an improved actuator system, of which afirst embodiment is generally indicated at 110. System 110 is shown inFIGS. 1 and 2 in a horizontal configuration. As shown, system 110generally includes as primary elements aircraft frame 120, shared link121, right actuator 141, left actuator 140, right drive arm 153, leftdrive arm 152, upper connecting rod 146, lower connecting rod 147, andflap 125.

Aircraft frame 120 acts as a reference structure upon which shared link121 is rotationally mounted through pivot joint 131. Right rotaryactuator 141 and left rotary actuator 142 are mounted on shared link121. Rotary actuators 141 and 142 are mounted with their drive shaftscoaxial and aligned along axis 144. In this embodiment, rotary actuators141 and 142 are permanent magnet electrical servo motors with planetarygear reduction units. However, other rotary actuators, such as steppermotors or rotary hydraulic actuators, may be used as alternatives.

Right actuator 141 forms pivot joint 133 with its output drive shaft143, which is rigidly coupled to one end of right actuator drive arm153. The other end of right actuator drive arm 153 is connected to oneend of lower connecting rod 147 through pivot joint 193. The other endof connecting rod 147 is connected to flap 125 through pivot joint 135.

Similarly, left actuator 140 forms pivot joint 134 with its output driveshaft 142, which is rigidly coupled to one end of left actuator drivearm 152. The other end of left actuator drive arm 152 is connected toone end of upper connecting rod 146 through pivot joint 194. The otherend of connecting rod 146 is connected to flap 125 through pivot joint136.

Flap 125 is rotationally coupled to aircraft frame 120 through pivotjoint 126. FIGS. 1 and 2 show flap 125 in a horizontal configuration, inwhich center line 127 of flap 125 is horizontal relative to airframe 120and thus generally parallel to horizontal reference line 130 of airframe120. In this horizontal configuration, left drive arm 152 and rightdrive arm 153 are aligned generally parallel to vertical axis 129 ofairframe 120. Right drive arm centerline 158 forms angle 163 with sharedlink centerline 122, which in this configuration is also equivalent toangle 164 between left drive arm 152 centerline 159 and shared linkcenterline 122. Shared linked 121 center line 122 forms angle 162 withhorizontal reference line 130 of airframe 120.

System 110 provides a linkage system with six movable rigid links (121,152, 153, 146, 147 and 125), eight pivot joints (131, 133, 134, 193,194, 135, 136 and 126), and two fixed reference points 120 a and 120 b.Note that left and right actuators 140, 141 are classified as pivotjoints 133, 134 in terms of the linkage system since their output shaftspivot about an axis of rotation, in this embodiment a common axis ofrotation 144. All of the pivot joints are orientated generally parallelto axis 144.

There are two linkage paths formed between first fixed reference point120 a and second fixed reference point 120 b, which together form thelinkage system. The first linkage path is defined, from airframereference 120 a to right airframe reference 120 b as pivot joint 131,shared link 121, left actuator 140 acting as pivot joint 134, drive arm152, pivot joint 194, upper connecting rod 146, pivot joint 136, flap125, and pivot joint 126. Such a linkage path is commonly referred to asa four member linkage since there are four rigid members. Similarly, thesecond linkage path is defined, from left airframe reference to rightairframe reference 120 b, as pivot joint 131, shared link 121, rightactuator 141 acting as pivot joint 133, drive arm 153, pivot joint 193,lower connecting rod 147, pivot joint 135, flap 125, and pivot joint126. The second linkage path is also a four member linkage. There areelements shared in both linkage paths, including pivot joint 131, sharedlink 121, flap 125, and shared pivot joint 126. In other words, three ofthe rigid members in each of the four member linkages are shared.

The linkage system contains two independent degrees of freedom. Morespecifically, the positions of all of the links and joints relative tothe reference (airframe 120) can be defined by two numbers. Bycontrolling the pivot joint angle 164 that left actuator 140 makes withshared link 121, and the pivot joint angle 163 that right actuator 141makes with shared link 121, one can independently control two degrees offreedom of the linkage system. The degrees of freedom of the linkagesystem and each linkage path will become more apparent in the followingsections discussing system 110 in various actuated configurations.

FIG. 3 shows system 110 in a configuration in which the system has beenactuated by the concerted effort of both left and right actuators 140and 141 in a dual motor actuation mode of operation. Flap 125 has beenrotated counter clockwise by angle 161 from the configuration shown inFIG. 1. Angle 162 that shared link 121 makes with airframe horizontalreference 130 has not changed from its angle in the horizontalconfiguration shown in FIGS. 1 and 2. Distance L1 between pivot joint136 and pivot 134 has been reduced by dL1 to L1′ and distance L2 betweenpivot joint 135 and pivot 133 has been increased by dL2 to L2′.

Right actuator 141 has caused right drive arm 153 to rotatecounterclockwise by angle 166 relative to shared link 121, decreasingangle 163 between right drive arm 153 and shared link centerline 122,and increasing distance L2 by dL2 to L2′. Similarly, left actuator 140has caused left drive arm 152 to rotate counterclockwise by angle 167relative to shared link 121 (which is equivalent to angle 166 in thissecond configuration), decreasing angle 164 between right drive arm 152and shared link centerline 122, and decreasing distance L1 by dL1 toL1′. Angle 164 between left drive arm 152 and shared link 121 has beendecreased by angle 167, such that angle 163 still equals angle 164.Right drive arm centerline 158 of right drive arm 153 and left drive armcenterline 159 of left drive arm 152 are still aligned with each otherbut are no longer aligned with reference vertical axis 129.

As right actuator 141 causes right drive arm 153 to rotatecounterclockwise, lower control rod 147 is forced rightwards. As controlrod 147 is forced rightwards, flap 125 is pushed rightwards at joint135, urging flap 125 to rotate counter clockwise. Similarly, as leftactuator 140 causes left drive arm 152 to rotate counterclockwise, uppercontrol rod 146 is forced leftwards. As control rod 146 is forcedleftwards, flap 125 is pulled leftwards at joint 136, also urging flap125 to rotate counter clockwise.

When both actuators are working normally in this dual motor actuationmode, right drive arm 153 will rotate counterclockwise 166 the samegeneral amount as left drive arm 152 rotates counter clockwise 167,causing the drive arms to remain generally parallel. Similarly, thereduction dL1 in distance L1 between pivot joint 136 and pivot 134 isabout the same amount as the increase dL2 in distance L2 between pivotjoint 135 and pivot 133. Because upper connecting rod 146 moves to theleft the same amount as lower connecting rod 147 moves to the right,shared link 121 remains substantially fixed in rotational positionrelative to air frame 120.

The dual motor actuation mode is effectively causing the linkage systemto act on flap 125 by both pushing and pulling at the same time, withone connecting rod pushing while the other connecting rod pulls. Whileactuator 141 pushes shared link 121 leftwards, actuator 140 pulls sharedlink 121 rightwards. The torque output of left actuator 140 and thetorque output of the right actuator 141 are both translated byconnecting rods 146 and 147 to act on moving flap 125. The linkagesystem is configured and arranged such that left and right actuators140, 141 contribute approximately equal torques on flap 125. However,there are other modes of operation, discussed in the following sections,in which the actuators provide unequal or opposing torques.

FIG. 4 shows system 110 in a configuration in which flap 125 has beenrotated clockwise by angle 161 from the configuration shown in FIG. 1.Drive arm 152 has been rotated clockwise by angle 167 such that drivearm 152 now forms angle 164 with shared link centerline 122. Drive arm153 has been rotated clockwise by angle 166 such that drive arm 153 nowforms angle 163 with shared link centerline 122. Angle 167 and angle 166are substantially equal such that drive arm 153 and drive arm 152 arestill parallel. Shared link 121 has not moved and still forms angle 162with reference horizontal 130. Distance L1 between pivot joint 136 andpivot 134 has been increased by dL1 to L1′ and distance L2 between pivotjoint 135 and pivot 133 has been decreased by dL2 to L2′.

System 110 is capable of continuing to operate after one of theactuators has jammed in a jam failure actuation mode. This jam failureconfiguration is shown in FIG. 5. In this configuration, right actuator141 is treated as having failed with a locked output shaft (i.e. closedfailure or jam), and system 110 has been actuated from the horizontalconfiguration shown in FIG. 1 by left actuator 140.

Because right actuator 141 has jammed, output shaft 143 is effectivelyrigidly coupled to shared link 121, and angle 163 between drive arm 153and shared link center line 122 will not change. Shared link 121,actuator 141, and drive arm 153 now form a single rigid member or link.The second linkage path through actuator 141, which was originally afour rigid member link with five pivot joints, is now a three memberlink with four pivot joints. The first linkage path through leftactuator 140 is still a four member link, since the actuator in its pathhas not jammed. The total linkage system is now defined by only onedegree of freedom. This single degree of freedom can be controlled bystill working left actuator 140.

As shown in FIG. 5, right drive arm centerline 158 of right drive arm153 and left drive arm centerline 159 of left drive arm 152 are nolonger in alignment. Since right actuator 141 has jammed, angle 163between right drive arm 153 and shared link centerline 122 is locked orjammed at the same angle relative to shared link centerline 122 as inthe horizontal configuration shown in FIGS. 1 and 2. However, left drivearm 152 has been moved clockwise by angle 167 relative to shared link122 to cause an increase in angle 164 between centerline 159 of leftdrive arm 152 and shared link centerline 122.

As left actuator 140 drives left drive arm 152 clockwise, upperconnecting rod 146 is pushed rightwards. As upper connecting rod 146 ispushed rightwards, flap 125 is pushed rightwards through joint 136. Thiswill urge flap 125 to rotate clockwise relative to air frame 120. Lowerconnecting rod 147 will move leftwards as flap 125 rotates clockwise.Since right actuator 141 is jammed, right drive arm 153 and shared link121 act as a single rigid body, and as lower connecting rod 147 movesleftwards, shared link 121 also must move leftwards (rotate clockwiseabout 131). Shared link 121 is rotated clockwise by angle 168 from itsold centerline position 172 to its current centerline position 122. Asshown in FIG. 5, in this configuration angle 162 between horizontalreference 130 and shared link centerline 122 has increased from angle162 in the configuration shown in FIG. 4.

Thus, even though right actuator 141 has jammed, left actuator is ableto actuate flap 125 clockwise and counter clockwise. Instead of havingtwo actuators pushing off each other, which keeps shared link 121 still,as in the dual actuation mode shown in FIG. 4, one actuator pushes offof shared link 121, and in response to the corresponding rotation ofshared link 121, a torque is provided to flap 125.

In this example, for a given rotation amount of left actuator 140, flap125 will rotate less than it would in the dual actuation mode, in whichboth left actuator 140 and right actuator 141 rotate. For example, incomparing FIG. 4 and FIG. 5, it can be seen that for an equivalentrotation of flap 125 by angle 161, angle 164, which drive arm 152 makeswith shared link centerline 122, is significantly greater in FIG. 5compared to FIG. 4.

System 110 can also be operated in a minimize backlash mode, in whichright actuator 141 and left actuator 140 are commanded to apply aconstant torque in opposition to each other in order to minimizebacklash experienced in actuating flap 125. In other words, bothactuators 140 and 141 may be configured to either always push or alwayspull against their respective connecting rods 146, 147, and flap 125 ismoved by controlling which actuator works harder.

For example, if operating in a minimize backlash mode in which bothactuator drive arms 152, 153 are configured to push against theircorresponding connecting rods 146, 147, respectively, right actuator 141is commanded to drive arm 153 counterclockwise with a small minimumtorque while left actuator 140 is commanded to drive arm 152 clockwisewith an equivalent minimum magnitude torque. In this case, connectingrods 146 and 147 will be constantly driven rightwards. This creates atension in the linkage system which will drive the internal contactinterfaces of all the joints to one side, such that backlash isminimized. To move flap 125, either actuator 140 or actuator 141,depending on the desired direction of rotation of flap 125, applies anincreased torque in order to push its connecting rod harder. Neitheractuator will be actuated to pull its corresponding connecting rod inthis mode (unless there is a failure condition which is beingaddressed). Alternatively, the minimize backlash mode may be implementedin the same manner but by directing the actuators to always pull theircorresponding connecting rod, instead of pushing. While the minimizebacklash mode may cause increased friction or power usage, it offers amethod of operating system 110 with virtually no backlash.

A configuration for operating system 110 in a modified performance modeis shown in FIG. 6. Modified performance mode provides a method ofvarying the mechanical advantage between system actuators 140, 141 andflap 125. Comparing the configurations shown in FIG. 6 to FIG. 1, eventhough flap 125 is positioned horizontally in both configurations, drivearms 152, 153 and shared link 121 have been adjusted in theconfiguration shown in FIG. 6. More specifically, shared link 121 hasbeen rotated clockwise by angle 168, drive arm 152 has been rotatedclockwise by angle 167, and drive arm 153 has been rotatedcounterclockwise by angle 166.

With this adjustment, the mechanical advantage between actuators 140,141 and flap 125 has been increased. This is perhaps most easilyobserved when considering the amount that control rod 146 moves to theright for a given clockwise rotation of drive arm 152. In FIG. 1, sincedrive arm 152 is perpendicular to drive connecting rod 146, a clockwiserotation of drive rod 152 will move connecting rod 146 to the right amaximal amount. Pivot joint 194 will move with only a horizontalcomponent. Comparing FIG. 1 to FIG. 6, since drive arm 152 makes anoblique angle with connecting rod 146 in the FIG. 6 configuration,rotation of drive arm 152 will cause both rightwards and downwardsmovement of pivot joint 136. Since the movement is “split” between bothhorizontal and vertical components, connecting rod 146 does not move asmuch to the right for a given angle of rotation of drive arm 152compared to the configuration shown in FIG. 1. Effectively, themechanical advantage in the linkage system is adjusted by varying angle162 that shared link 121 makes with airframe 120 horizontal reference130. By being able to adjust the mechanical advantage, flightcharacteristics can be modified, such as the maximum rate of movement offlap 125, the maximum angular displacement of flap 125, the backlash,the maximum torque that can be applied to flap 125, and the naturalresonant frequency of the system.

As shown in FIGS. 1-6, system 110 has two independent degrees offreedom. In other words, given a fixed reference air frame 120, thepositions of all other elements and pivot joints can be defined by twoindependent variables, X and Y, in which X and Y may be variedindependently from each other. For example, angle 161 between flap 125centerline 127 and horizontal reference 128, and angle 162 betweenhorizontal reference 130 and shared link center line 122 define twoindependent variables specifying the two degrees of freedom in thesystem. Flap angle 161 can be varied independently of shared link angle162, as shown in the configuration in FIG. 3. Alternatively, shared linkangle 162 can be adjusted as the flap angle 161 is held constant, asshown in the configuration in FIG. 6. Thus, flap angle 161 and sharedlink angle 162 are independent variables. For a given flap angle 161 andshared link angle 162, angles 163 and 164 of drive arms 152 and 153 arefixed. There are only two degrees of freedom in the system, such that iftwo degrees are held constant (angle 161 and 162), the whole system isfixed. One can alternatively define angles 163 and 164. For a givenangle 163 and angle 164, flap angle 161 and shared link angle 162 arefixed. Left actuator 140 is arranged to directly control angle 164.Similarly, right actuator 141 controls angle 163. By being able tocontrol actuator angles 140 and 141, and therefore actuator angles 163and 164, one can control flap angle 161 and shared link angle 162.Because there are two degrees of freedom, even if one of the actuatorsbecomes locked, making the system now a single degree of freedom system,the other actuator can still cause a change in flap angle 161.

In general, system 110 has a mechanical linkage which is made up of twopartially dependent linkage paths. Each linkage path has two degrees offreedom. The linkage paths share one degree of freedom (angle 121). Eachlinkage path has an actuator along its path that controls one of itsdegrees of freedom. By controlling both actuators, all degrees offreedom of the system are defined. If one of the degrees of freedombecomes locked, the other degree of freedom in the system can be used tochange the angle of the flap. This results in jam resistance. Also, byhaving a second degree of freedom, the degree of freedom which isindependent of the flap angle can be used to adjust the mechanicaladvantage of the system, or to test the system during use withoutadjusting the flap angle.

A second embodiment 210 of the system is shown in FIGS. 7 and 8. In thisembodiment, the drive arms 152, 153 and connecting rods 146, 147 insystem 110 have been replaced by linear spindles 296 and 297. Similar tofirst embodiment 110, system 210 is defined by a mechanical linkagehaving two linkage paths between two positions 220 a, 220 b on reference220. The first linkage path is defined from reference 220 a to reference220 b and comprises pivot joint 231, shared link 221, pivot joint 233,linear spindle 297, pivot joint 235, flap 225, and pivot joint 226. Thesecond linkage path also is defined from reference 220 a to reference220 b but comprises pivot joint 231, shared link 221, pivot joint 234,linear spindle 296, pivot joint 236, flap 225, and pivot joint 226.Linear spindle 296 allows the distance L1 between joint 234 and pivotjoint 236 to be adjusted. Similarly, linear spindle 297 allows thedistance L2 between pivot joint 233 and pivot joint 235 to be adjusted.Each linear spindle acts as an independent degree of freedom in themechanical linkage system of embodiment 210.

System 210 can be operated in the dual motor actuation mode describedfor system 110. For example, if linear spindle 296 is shortened whilelinear spindle 297 is elongated, flap 225 will be rotated clockwisewhile shared link 221 remains still.

Additionally, system 210 will continue to work in the jam failureactuation mode described for system 110. For example, if linear spindle297 jams, adjustment of linear spindle 296 will continue to change theangle of flap 225, since rotation of shared link 221 will allow theposition of pivot joint 235 to change.

A third embodiment 310 of the system is shown in FIG. 9. System 310 isidentical to system 110 but with the addition of spring 382, damper 383,and brake 381. Spring 382 is positioned between shared link 321 andairframe reference 320 c. In the horizontal configuration shown in FIG.9, spring 382 is in an uncompressed state. However, any movement ofshared link 321 from its position in FIG. 9 will cause spring 382 toapply a restoring force or torque. Spring 382 may be a linear coilspring, a flexure, or a torsional spring arranged about pivot joint 331.Spring 382 may alternatively be placed about pivot joint 326. Damper 383is arranged to dampen the rotation of shared link 321 relative toreference structure 320. Spring 382 and damper 383 are useful forchanging the operating dynamics of the system, such as reducing backlashand vibration.

Brake 381 is arranged to lock the position of shared link 321 relativeto reference 320. When system 310 is operating in dual motor actuationmode, operation of system 310 is substantially equivalent to theoperation of system 110. The effect of spring 382, damper 383, and brake381 is important when an open failure occurs in one of the actuators. Anopen failure is when the actuator is no longer capable of applying atorque to its output shaft, and is in contrast to the jammed actuatorfailure described above with references to FIG. 5. An open failure insystem 110 is problematic because, without brake 381, flap 125 would befree to move up and down regardless of the action of the remainingworking actuator. This is due to the fact that the system is a twodegree of freedom system, and when one degree of freedom is uncontrolled(i.e. open actuator failure) the complete kinematic state of the systemcan not be controlled. However, because of brake 381 in system 310, anopen failure can be handled. If an open failure occurs, brake 381 isactivated to lock shared link 321, effectively converting the linkagesystem into a single degree of freedom system. The single degree offreedom system can then be actuated by the remaining working actuator tocontrol flap 325, as described with reference to FIG. 5.

A fourth embodiment 410 is shown in FIG. 10. In this embodiment, thedrive arm configuration has been inverted. More specifically, drive arm452 and drive arm 453 are arranged on the same side of a horizontalreference line extending through the axis of rotation 443 of actuator441 and pivot joint 426. In this configuration, the torque that actuator441 applies to drive arm 453 is reversed compared to the previousconfigurations. For example, referring to FIG. 10, when drive arm 453pushes rightward against connecting rod 447, a counteracting counterclockwise torque is applied to shared link 421. In comparison, referringto FIG. 9, as drive arm 353 pushes rightward on connecting rod 347, acounteracting clockwise torque is applied to shared link 321. As drivearm 453 pushes rightward against connecting rod 447 and applies acounter clockwise torque on shared link 421 as described, drive arm 452pulls leftward on connecting rod 446, and applies a counteractingclockwise torque on shared link 421. The counter clockwise torqueapplied to shared link 421 by drive arm 453 is canceled by the clockwisetorque applied by drive arm 452. This allows for reallocating mechanicalstrain on the mechanical linkage system.

A fifth embodiment 510 is shown in FIGS. 11-13. System 510 is optimizedas a stand alone package that can be easily transported and replaced asa line replaceable unit. More specifically, system 510 includes its ownreference 520, which merely needs to be affixed to an external referencesuch as an airframe. There is no longer a need to mount multiple pointsof the linkage system to an external reference. Also, shared link 521 insystem 510 is now mounted with an axis of rotation which is coincidentwith the axis of rotation of actuators 540 and 541. Also, system 510 hasan inverted connecting rod structure.

Reference frame 520 of system 510 acts as the linkage system referencestructure. Shared link 521 is a small disk to which left rotary actuator540 and right rotary actuator 541 are mounted. Right actuator outputshaft 543 passes through bearing joint 531 of frame 520. Thus, rightoutput shaft 543 is arranged to rotate about axis 544 relative to frame520. Similarly, left output shaft 542 passes through bearing joint 532of frame 520 and is arranged to rotate about axis 544 relative to frame520. Shared link 521 may be configured to rotate about axis 544 togetherwith the stators of actuator 540 and 541. In other words, output shafts542 and 543 can be held fixed relative to frame 520 while shared link521, actuator 540, and actuator 541 all rotate together relative frame520.

Drive arm 553 is rigidly mounted on output shaft 543, and drive arm 552is rigidly mounted on output shaft 542. Drive arm 553 connects toconnecting rod 547 through pivot joint 593. Similarly, drive arm 552connects to connecting rod 546 through pivot joint 594. Connecting rod546 connects to receiving arm 556 through pivot joint 536. Similarly,connecting rod 547 connects to receiving arm 555 through pivot joint535. Receiving arm 555 and receiving arm 556 are both rigidly mounted tosystem output shaft 525. In other words, arms 555 and 556 do not rotateseparately from shaft 525. Output shaft 525 is configured to drive anexternal load, such as an aircraft flap.

Due to the similarity in the inverted connecting rods, the operation ofsystem 510 is similar to system 410. For example, with reference to FIG.12, in order to drive system output shaft 525 clockwise, drive arm 553should push rightwards on connecting rod 547 and drive arm 552 shouldpush also rightwards on connecting rod 546. The torque applied by rightactuator 541 on drive arm 553 is equal and opposite the torque appliedon drive arm 552 by left actuator 540. Since the torques applied byactuator 540 and 541 cancel each other out, shared link 521 does notrotate relative to frame 520 as output shaft 525 is rotated clockwise.

In the event of a jam failure of one of the actuator, the other actuatorwill continue working, as in system 110 and described with reference toFIG. 5. However, shared link 521 (along with actuators 540 and 541) willrotate relative to frame 520 as output shaft 525 rotates. In order tohandle open actuator failures, a brake, spring, or damper is placedbetween shared link 521 and reference frame 520, as described in system410.

A sixth embodiment 610 is shown in FIGS. 14-17. In this embodiment,shared link 621 has been configured for sliding engagement with frame620. As shown, frame 620 has opening 609, which is configured to receiveshared link 621 in sliding engagement. Shared link 621 does not rotaterelative to frame 620. During dual motor actuation mode operation,shared link 621 does not slide relative to frame 620. However, in jamfailure operation mode, left and right movement of shared link 621relative to frame 620 provides the linkage system with the necessarydegree of freedom to continue to operate through the jam failure.

Seventh embodiment system 710 is shown in FIGS. 18-24. System 710 isvery similar in general structure and operation to fifth embodimentsystem 510 shown in FIGS. 11-13. However, system 710 has larger bearings726 a and 726 b supporting system output shaft 725 in rotatingengagement with frame 720. Similarly, bearings 733 and 734 supportactuators 740 and 741 and shared link 721 in pivoting relationship withframe 720. System 710 provides a compact, line replaceable unit withhigh mean time between failure.

As shown in FIGS. 18 and 19, actuator system 710 comprises as primaryelements frame 720, system output shaft 725, right actuator 740, leftactuator 741, shared link 721, drive arm 752, drive arm 753, connectingrod 746, and connecting rod 747.

Frame 720 acts as both a housing and a reference structure upon whichthe actuator system bearings interact. For example, shared link 210 ismounted by bearings 733 and 734 for rotary motion relative to frame 720about axis 744. Actuators 740 and 741 are mounted upon shared link 721,and also have their output shaft axes of rotation coincident with axis744. Actuators 740 and 741 are rotary motors with output planetary gearstages. Output shaft 742 of right actuator 740 is splined and rigidlycoupled to drive arm 752. Right drive arm 752 is connected to the leftside of connecting rod 746 through pivot joint 794. The right side ofconnecting rod 746 is coupled to drive arm 756 through pivot joint 736.Drive arm 756 is rigidly coupled to system output shaft 726. Systemoutput shaft 726 is mounted to frame 720 through bearings 726 a and 726b for rotary movement about axis 726. Output shaft 743 of actuator 741is splined and rigidly connected to drive arm 753. Drive arm 753 isconnected to connecting rod 747 through pivot joint 793. Connecting rod747 is connected to drive arm 755 through pivot joint 793. Drive arm 755is rigidly coupled to system output shaft 725.

The operation of system 710 is similar to operation of the otherembodiments. Each actuator controls a single degree of freedom in a twodegree of freedom system. In system 710, actuators 740 and 741 torqueoff of each other across shared link 721 in order to both cause a pushforce or both cause a pull force on connecting rods 746 and 747. Inother words, actuator 740 is driven to apply a torque equal and oppositeto shared link 721 as the torque applied by actuator 741. As viewed fromthe perspective in FIG. 18, if the torque applied by actuator 740 causesa clockwise torque on shared link 721 (which causes connecting rod 746to be pushed rightwards), actuator 741 will be driven to cause acounterclockwise torque on shared link 721 (which causes a rightwardsforce pushing on connecting rod 747). System output shaft 725 will thusbe driven clockwise, while shared link 721 experiences no net torque.

The bearing configuration of system 710 is shown in FIG. 20. Outersheath 701 acts as a unitary member with frame 720. Bearings 702 allowcylinder 703 to rotate about axis 744 relative to frame 720. Bearings705, held in place by cylinder 704, allow inner cylinder 706 to alsorotate about axis 744 relative to frame 720. Planetary gears 707 operatebetween inner cylinder 706 and gear carrier 708.

System 710 has a very compact form factor with relatively large bearingsfor the overall size of system 710. Having relatively large bearingshelps produce a system with a particularly high estimated mean timebetween failures.

The disclosed actuator system and method resulted in several surprisingadvantages. The disclosed actuator system is smaller, lighter, andfaster than current hydraulic actuators. The disclosed actuator systemuses power only when needed, and does not have the continuous wasteassociated with maintaining a hydraulic high pressure and compensatingfor hydraulic valve leakage. Additionally, electronic actuator controlsprovide higher bandwidth control than is possible with a hydraulicvalve. Further, complex seals necessary in hydraulic actuators are notneeded in the disclosed actuator system and method.

The disclosed actuator system and method, due to its novel and uniquestructure, continues to work through a jam failure. The jam failurehandling works inherently in the disclosed system, without a need forrelease clutches. Additionally, the disclosed actuator system can beconfigured with a single brake to be able to handle an open actuatorfailure in either actuator. Current redundant electromechanicalactuators need two brakes in order to handle an open failure in eithersystem.

Further, the disclosed actuator system and method inherently increasesactuator lifetime, since each actuator will typically provide only halfof the work provided by the actuator system. The disclosed actuatorsystem will continue working through either an actuator jam failure oran actuator open failure, and the malfunctioning actuator can be easilyreplaced at a later time after further operation. The disclosed actuatorsystem also provides the novel ability to be able to adjust themechanical advantage of the system during operation. Further, a mode ofoperation is provided in the disclosed system in which backlash can beminimized. The dual degree of freedom nature of the system also allowsfor the ability to conduct system self tests during operation, withoutneeding to change the actuator output. All of these advantages andvaried modes of operation are available real time in the disclosedsystem, i.e. the system does not need to be shut down and stopped inorder to be reconfigured.

Various alternative embodiments of the disclosed actuator system andmethod are also possible. For example, the motors can be configured tooperate with dynamic braking or regeneration. The motor drivers, dynamicbraking resistor, and regeneration capacitor can be combined with thedisclosed embodiments. Additionally, position sensors, such as encodersor resolvers, can be added at some of the pivot joints together with aservo controller to form a complete servo system. Heat sensors can beadded to help detect and diagnose bearing and/or motor malfunction.Torque sensors can be added to the output or drive shafts to providefurther operation monitoring and feedback signals.

Therefore, while the presently-preferred form of the actuator system andmethod has been shown and described, and several modificationsdiscussed, persons skilled in this art will readily appreciate thatvarious additional changes may be made without departing from the scopeof the invention.

The invention claimed is:
 1. An actuator system comprising: an elementconfigured for rotary movement about a first axis relative to areference structure; a linkage system connected to said element and saidreference structure; said linkage system having a link configured forrotary movement about a second axis relative to said referencestructure; said first axis and said second axis being substantiallyparallel and operatively offset a substantially constant distance; saidlinkage system configured and arranged such that a first angle ofrotation between said element and said reference structure may be drivenindependently of a second angle of rotation between said link and saidreference structure; a first rotary actuator connected to said linkagesystem and arranged to rotationally control a first degree of freedom ofsaid linkage system; a second rotary actuator coupled to said linkagesystem and arranged to rotationally control a second degree of freedomof said linkage system, said first degree of freedom and said seconddegree of freedom being independent degrees of freedom; wherein saidfirst actuator is configured and arranged to drive rotation of saidelement about said first axis when said second degree of freedom isoperatively locked.
 2. The actuator system as set forth in claim 1,wherein said linkage system comprises: a first linkage connected to saidelement at a first element connection offset from said second axis andextending from said first element connection to a first memberconnection offset from said first axis; a second linkage connected tosaid element at a second element connection offset from said second axisand extending from said second element connection to a second memberconnection offset from said first axis; a first member connected to saidfirst linkage and said first rotary actuator; said first memberconfigured and arranged for rotary movement about a third axis relativeto said link; a second member connected to said second linkage and saidsecond rotary actuator; and said second member configured and arrangedfor rotary movement about a fourth axis relative to said link.
 3. Theactuator system as set forth in claim 2, wherein: said first rotaryactuator is configured and arranged to control rotation of said firstmember; said second rotary actuator is configured and arranged tocontrol rotation of said second member; said first rotary actuator, saidfirst member and said first linkage are configured and arranged torotate said element about said second axis relative to said referencestructure when said second rotary actuator operatively locks rotation ofsaid second member about said fourth axis relative to said link; andsaid link, said first and second members and said first and secondrotary actuators configured and arranged such that said link rotatesabout said first axis when said second rotary actuator operatively locksrotation of said second member about said fourth axis relative to saidlink.
 4. The actuator system as set forth in claim 2, wherein saidfirst, second, third, and fourth axis are substantially parallel to eachother.
 5. The actuator system as set forth in claim 2, wherein saidfirst member connection and said second member connection are positionedon opposite sides of an imaginary line through said first axis and saidsecond axis or said first element connection and said second elementconnection are positioned on the same side of an imaginary line throughsaid first axis and said second axis.
 6. The actuator system as setforth in claim 2, wherein said third axis is coincident with said fourthaxis.
 7. The actuator system as set forth in claim 6, wherein said firstaxis is coincident with said third axis.